/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.message;

import java.util.List;
import java.util.NoSuchElementException;

import org.apache.http.Header;
import org.apache.http.HeaderIterator;

/**
 * Implementation of a {@link HeaderIterator} based on a {@link List}. For use
 * by {@link HeaderGroup}.
 * 
 * @since 4.0
 */
public class BasicListHeaderIterator implements HeaderIterator {

	/**
	 * A list of headers to iterate over. Not all elements of this array are
	 * necessarily part of the iteration.
	 */
	@SuppressWarnings("rawtypes")
	protected final List allHeaders;

	/**
	 * The position of the next header in {@link #allHeaders allHeaders}.
	 * Negative if the iteration is over.
	 */
	protected int currentIndex;

	/**
	 * The position of the last returned header. Negative if none has been
	 * returned so far.
	 */
	protected int lastIndex;

	/**
	 * The header name to filter by. <code>null</code> to iterate over all
	 * headers in the array.
	 */
	protected String headerName;

	/**
	 * Creates a new header iterator.
	 * 
	 * @param headers
	 *            a list of headers over which to iterate
	 * @param name
	 *            the name of the headers over which to iterate, or
	 *            <code>null</code> for any
	 */
	public BasicListHeaderIterator(@SuppressWarnings("rawtypes") List headers,
			String name) {
		if (headers == null) {
			throw new IllegalArgumentException("Header list must not be null.");
		}

		this.allHeaders = headers;
		this.headerName = name;
		this.currentIndex = findNext(-1);
		this.lastIndex = -1;
	}

	/**
	 * Determines the index of the next header.
	 * 
	 * @param from
	 *            one less than the index to consider first, -1 to search for
	 *            the first header
	 * 
	 * @return the index of the next header that matches the filter name, or
	 *         negative if there are no more headers
	 */
	protected int findNext(int from) {
		if (from < -1)
			return -1;

		final int to = this.allHeaders.size() - 1;
		boolean found = false;
		while (!found && (from < to)) {
			from++;
			found = filterHeader(from);
		}
		return found ? from : -1;
	}

	/**
	 * Checks whether a header is part of the iteration.
	 * 
	 * @param index
	 *            the index of the header to check
	 * 
	 * @return <code>true</code> if the header should be part of the iteration,
	 *         <code>false</code> to skip
	 */
	protected boolean filterHeader(int index) {
		if (this.headerName == null)
			return true;

		// non-header elements, including null, will trigger exceptions
		final String name = ((Header) this.allHeaders.get(index)).getName();

		return this.headerName.equalsIgnoreCase(name);
	}

	// non-javadoc, see interface HeaderIterator
	@Override
	public boolean hasNext() {
		return (this.currentIndex >= 0);
	}

	/**
	 * Obtains the next header from this iteration.
	 * 
	 * @return the next header in this iteration
	 * 
	 * @throws NoSuchElementException
	 *             if there are no more headers
	 */
	@Override
	public Header nextHeader() throws NoSuchElementException {

		final int current = this.currentIndex;
		if (current < 0) {
			throw new NoSuchElementException("Iteration already finished.");
		}

		this.lastIndex = current;
		this.currentIndex = findNext(current);

		return (Header) this.allHeaders.get(current);
	}

	/**
	 * Returns the next header. Same as {@link #nextHeader nextHeader}, but not
	 * type-safe.
	 * 
	 * @return the next header in this iteration
	 * 
	 * @throws NoSuchElementException
	 *             if there are no more headers
	 */
	@Override
	public final Object next() throws NoSuchElementException {
		return nextHeader();
	}

	/**
	 * Removes the header that was returned last.
	 */
	@Override
	public void remove() throws UnsupportedOperationException {

		if (this.lastIndex < 0) {
			throw new IllegalStateException("No header to remove.");
		}
		this.allHeaders.remove(this.lastIndex);
		this.lastIndex = -1;
		this.currentIndex--; // adjust for the removed element
	}
}
